Switchable gear device

ABSTRACT

The present disclosure relates to a switchable gear device and to various arrangements and systems including the switchable gear device, such as a transfer gearbox for 2WD to 4WD conversion and a lock device for a static position, such as for use in a folding multi-position ladder. In another application, the switchable gear device is applied to articulated components configured to undergo movement relative one another.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 62/816,947, filed on Mar. 12, 2019.

TECHNICAL FIELD

The present disclosure relates to gear devices, and more specifically to a switchable gear device. The present disclosure also relates to various arrangements and systems including the switchable gear device, such as a transfer gearbox for 2WD to 4WD conversion and a stop or lock device for a static position, such as a lock device for a folding multi-position ladder, as well as for different types of mechanisms employing articulated arms and related mechanical applications.

BACKGROUND

Switchable gear devices are used for many mechanical applications. However, existing switchable gear devices are inefficient in operation and typically require a large space when implemented in mechanical applications, which often increases the overall weight of the resulting device. Conventional switchable gear devices are also not adapted or configured for various types of mechanical applications.

Therefore, it is desirable to provide a switchable gear device which exhibits high operational efficiency, is adapted for various types of mechanical applications, and is configured to reduce the space and overall weight required for various types of mechanical applications.

SUMMARY

A switchable gear device is described. The switchable gear device includes an internal gear and an external case configured to receive the internal gear. The external case is configured to be drivingly connected to and disconnected from an external rotational shaft via the internal gear. When received within the external case, the internal gear is configured to be selectively switched between an “ON” state and an “OFF” state. In the “ON” state of the internal gear, the external case is connected to the external rotational shaft for undergoing rotation therewith (i.e., the external case transmits the rotation of the external rotation shaft). In the “OFF” state of the internal gear, the external case is disconnected from the external rotational shaft and does not undergo rotation therewith (i.e., the external case does not transmit the rotation of the external rotation shaft).

According to a feature of the present disclosure, the internal gear and external case are configured so as to allow the internal gear to slide within and relative to the external case to be selectively placed between the “ON” and “OFF” states.

The internal gear is provided with a plurality of external gear teeth and the external case is provided with a plurality of gear slots for meshing engagement with the respective external gear teeth of the internal gear. The meshing engagement between the external gear teeth and gear slots is such that the gear teeth are configured to slide along the respective gear slots to selectively place the internal gear between the “ON” and “OFF” states.

The internal gear can be readily switched to the “ON” state by sliding the internal gear relative to the external case to a first position in which the internal gear is brought into engagement with the external rotational shaft to transmit rotational movement of the external rotational shaft to the external case. The internal gear can be readily switched from the “ON” state to the “OFF” state by sliding the internal gear relative to the external case to a second position in which the internal gear is disengaged from the external rotational shaft so that the rotational movement of the external rotational shaft is not transmitted to the external case.

The internal gear has a tubular configuration and is provided with a plurality of internal gear teeth for meshing engagement with respective external gear teeth of the external rotational shaft when the internal gear is in the first position relative to the external case (i.e., when the internal gear is placed in the “ON” state).

In one embodiment, the internal gear is switched between the “ON” state and the “OFF” state by a hydraulic system (hydraulic pressure device) incorporated to the external case and the internal gear. Alternatively, the internal gear is switched between the “ON” state and the “OFF” state by an electro-magnetic system incorporated to the external case and the internal gear.

In one application according to the present disclosure, the switchable gear device is a transfer gearbox for 2WD to 4WD conversion.

In another application according to the present disclosure, the switchable gear device is used like a stop or lock device for a static position. In one implementation, the switchable gear is incorporated in a folding multi-position ladder.

In another application according to the present disclosure, the switchable gear device is applied to articulated components configured to undergo movement relative one another.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a switchable gear device according to an embodiment of the present disclosure.

FIG. 2 is a right-side exploded view showing the internal gear and external case of the switchable gear device along with an external rotational shaft to which the external case is configured to be connected to and disconnected from via the internal gear.

FIG. 3 is a perspective of the exploded view in FIG. 2.

FIG. 4 is another perspective of the exploded view in FIG. 2.

FIG. 5 is another perspective of the exploded view in FIG. 2.

FIG. 6 is a side perspective view showing the assembly of the internal gear relative to the external case and the external rotational shaft.

FIG. 7 is rear perspective view of the assembly in FIG. 6.

FIG. 8 is a right-side view showing the switchable gear device in which the internal gear switched to the “ON” state, and with the external case being depicted in semi-transparent form to allow observation of the internal gear.

FIG. 9 is a rear perspective view of FIG. 8.

FIG. 10 is a cross-sectional side view taken along a horizontal line cutting through the center of the device shown in FIG. 8.

FIG. 11 is a rear cross-sectional perspective view of FIG. 10.

FIG. 12 is a right-side view showing the switchable gear device in which the internal gear switched to the “OFF” state, and with the external case being depicted in semi-transparent form to allow observation of the internal gear.

FIG. 13 is a rear perspective view of FIG. 12.

FIG. 14 is a cross-sectional side view taken along a horizontal line cutting through the center of the device shown in FIG. 12.

FIG. 15 is a rear cross-sectional perspective view of FIG. 14.

FIG. 16 is a side perspective view illustrating an application of the switchable gear device as a transfer gear box for 2WD to 4WD conversion.

FIG. 17 is a side perspective view of FIG. 16.

FIG. 18 is an upper perspective view of FIG. 16.

FIG. 19 is a cross-sectional side view showing the switchable gear device activated by a hydraulic pressure device and the internal gear in the “ON” state.

FIG. 20 is a rear cross-sectional perspective view of FIG. 19.

FIG. 21 is a cross-sectional side view showing the switchable gear device deactivated by the hydraulic pressure device and the internal gear in the “OFF” state.

FIG. 22 is a rear cross-sectional perspective view of FIG. 21.

FIG. 23 is a diagrammatic view illustrating a conventional lock device in the closed state.

FIG. 24 is a diagrammatic view illustrating a conventional lock device in the open state.

FIG. 25 is a cross-sectional side view illustrating an application of the switchable gear device as a lock device with the internal gear shown in the “ON” (closed) state.

FIG. 26 is a rear cross-sectional perspective view of FIG. 25.

FIG. 27 is a cross-sectional side view similar to FIG. 25, but with the internal gear shown in the “OFF” (open) state.

FIG. 28 is a rear cross-sectional perspective view of FIG. 27.

FIG. 29 is a top perspective view illustrating the various angular positions which can be achieved by the lock device incorporating a switchable gear device according to the present disclosure.

FIG. 30 illustrates various exemplary locations for the locking device according to the present disclosure in a folding multi-position ladder.

FIG. 31 is a perspective view illustrating a switchable gear device according to the present invention applied to articulated arms.

FIG. 32 is a top view of the switchable gear device shown in FIG. 31.

FIG. 33 is a perspective view similar to FIG. 31, with the articulated arms of the switchable gear device in a disconnected state.

FIG. 34 is a top, partially exploded perspective view of the switchable gear device shown in FIG. 32.

FIG. 35 is a left perspective view of the switchable gear device shown in FIG. 34.

FIG. 36 a right perspective view of the switchable gear device shown in FIG. 34.

FIG. 37 is a side view in perspective of the switchable gear device shown in FIG. 34.

FIG. 38 is another exploded view in perspective illustrating a main shaft and switchable gear removed from one of the articulated arms of the switchable gear device.

FIG. 39 is a right perspective view of the switchable gear device shown in FIG. 38.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary aspects and embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

FIGS. 1-7 show various front, right side, exploded, and perspective views illustrating a switchable gear device, generally designated at 10, according to an embodiment of the present disclosure. As shown in FIG. 1, switchable gear device 10 includes a gear connector or switchable gear 12 (hereinafter also “internal gear”) and an external gear or output shaft 14 (hereinafter also “external case”) configured to receive internal gear 12. Internal gear 12 is provided with external gear teeth 12 a and external case 14 is provided with gear slots 14 a for meshing engagement with respective external gear teeth 12 a of internal gear 12. Internal gear 12 and external case 14 are configured so as to allow the internal gear 12 to slide within and relative to external case 14. Internal gear 12 has a tubular configuration and is provided with internal gear teeth 12 a.

Referring to FIGS. 2-6, external case 14 is configured to be drivingly connnected to and disconnected from a main shaft 16 (hereinafter also “external rotational shaft”) via internal gear 12. The driving connection or engagement is accomplished by bringing internal gear teeth 12 a of internal gear 12 into meshing engagement with external gear teeth 16 a of main shaft 16.

When received within external case 14, internal gear 12 is configured to be selectively switched between an “ON” state and an “OFF” state. In the “ON” state of internal gear 12, external case 14 is connected to main shaft 16 for undergoing rotation therewith (i.e., external case 14 transmits the rotation of main shaft 16). In this “ON” state configuration, external gear teeth 12 a of internal gear 12 engage gear slots 14 a of external case 14, and internal gear teeth 12 b of internal gear 12 engage external gear teeth 16 a of main shaft 16. In the “OFF” state of internal gear 12, external case 14 is disconnected from main shaft 16 and does not undergo rotation therewith (i.e., external case 14 does not transmit the rotation of main 16). In this “OFF” state configuration, external gear teeth 12 a of internal gear 12 continue to engage gear slots 14 a of external case 14, however, internal gear teeth 12 b of internal gear 12 are disengaged from external gear teeth 16 a of main shaft 16. Stated otherwise, in the “OFF” state, external case 14 can rotate freely.

The disengagement of internal gear teeth 12 b from external gear teeth 16 a described above is accomplished by sliding movement of internal gear 12 within and relative to external case 14. Thus, according to a feature of the present disclosure, internal gear 12 and external case 14 are configured so as to allow internal gear 12 to slide within and relative to external case 14 to selectively place internal gear 12 between the “ON” and “OFF” states.

More specifically, internal gear 12 can be readily switched to the “ON” state by sliding internal gear 12 relative to external case 14 to a first position within external case 14 in which internal gear teeth 12 b of internal gear 12 are brought into meshing engagement with external gear teeth 16 a of external rotational shaft 16 to transmit rotational movement of external rotational shaft 16 to external case 14 via internal gear 12. Internal gear 12 can be readily switched from the “ON” state to the “OFF” state by sliding internal gear 12 relative to external case 14 to a second position within external case 14 until internal gear teeth 12 b of internal gear 12 disengage from external gear teeth 16 a of external rotational shaft so that rotational movement of external rotational shaft 16 is not transmitted to external case 14 via internal gear 12.

FIGS. 8-11 show various right side, rear, perspective and cross-sectional views of switchable gear device 10 in which internal gear 12 is in the “ON” state (i.e., internal gear 10 is connected to external rotational shaft 16). FIGS. 12-15 show various right side, rear, perspective and cross-sectional views of switchable gear device 10 in which internal gear 12 is in the “OFF” state (i.e., internal gear 12 is disconnected from external rotational shaft 16), thereby enabling external case 14 to rotate freely. In FIGS. 8, 9, 12 and 13, external case 14 is depicted in semi-transparent form to allow observation of internal gear 12.

It will be appreciated that switchable gear device 10 is readably switchable “ON” and “OFF” as described above to connect one gear (i.e., external case 14) to another (i.e., external rotational shaft 16). The configuration (e.g., shape) of switchable gear device 10, including internal gear 12 positionable inside of external case 14 and adapted for sliding movement therein to achieve the “ON” and “OFF” states, effectively reduces the space required for this type of mechanical application, thus reducing the overall weight of the resulting mechanical system in which switchable gear device 10 is applied. Furthermore, since the gear connection between internal gear 12 and external rotational shaft 16 is internal (i.e., inside of external case 14), the resulting mechanical system is able to operate with high efficiency, particularly because it results in a coupling configured to operate as one single, integral piece.

FIGS. 16-18 are perspective views illustrating an application of the switchable gear device in an engine transfer gear box or transfer case for 2WD to 4WD conversion. In these figures, external case 14 is depicted in semi-transparent form to allow observation of internal gear 12.

The arrangement of the transfer case in FIGS. 16-18 illustrates the interconnection and relative positions between switchable gear device 10 (internal gear 12 and external case 14), external rotation shaft 16 (main shaft), first output shaft (4WD) 17, second output shaft (2WD) 18 and corresponding gears 20 and 22. In this configuration, gear device 10 is connected to an engine itself represented by external rotation shaft 16 (main shaft) as described above with reference to FIGS. 2-7. Alternatively, gear device 10 can be connected to a rotor or gear that brings the power of an engine. The function of gear device 10 is to transmit the movement of rotation of an engine when gear device 10 is in the “ON” state (FIGS. 8-11) and to discontinue its rotation when gear device 10 is in the “OFF” state.

More specifically, the function of the arrangement shown in FIGS. 16-18 is as a shift shaft. Internal gear 12 slides into external case 14 to achieve the “ON” state (FIGS. 8-11) in which external case 14 is connected to first output shaft (4WD) 17 to transmit rotation for 2WD/4WD conversion. When internal gear 12 is to be placed in the “OFF” state, internal gear 12 is slid out from first output shaft (4WD) 17 and external case 14 is disconnected from first output shaft (4WD) 17 so that external case 14 can rotate freely (FIGS. 12-15).

By the foregoing arrangement shown in FIGS. 16-18, gear device 10 functions as a switchable interior gear that is switchable “ON” and “OFF” to connect one gear (i.e., external case 14) to another (i.e., first output shaft (4WD) 17) in the “ON” state and disconnect these two gears from each other in the “OFF” state. The design and shape of this configuration, including the internal gear connection and reduction in space as described above, makes this arrangement more effective as compared to conventional transfer gearbox arrangements. Since the connection of the gear is internal, the overall efficiency of the mechanical system is increased because the resulting coupling operates integrally as one piece as internal gear 12 is contained outside by external case 14 and inside by first output shaft (4WD) 17.

FIGS. 19-22 are cross-sectional side and perspective views illustrating a mechanism for activating switchable gear device 10, according to an exemplary embodiment of the present disclosure.

In FIGS. 19-22, internal gear 12 of gear device 10 is activated (i.e., placed between the “ON” and “OFF” states as described above) by means of a hydraulic system including a hydraulic piston 24 operated by a pressure device 26 with pressure in 28 and pressure out 28 ports. FIGS. 19 and 20 illustrate the configuration in which internal gear 12 is in the “ON” state, in which external case 14 is connected to first output shaft (4WD) 17 for transmission of rotation as described above. FIGS. 21-22 illustrate the configuration in which internal gear 12 is in the “OFF” state, in which external case 14 is not connected to first output shaft (4WD) 17 and external case 14 is able to rotate freely as described above.

It will be appreciated that the mechanism for activating switchable gear device 10 is not limited to a hydraulic system. For example, switchable gear device 10 can be activated by an electro-magnetic system or other suitable activation means without departing from the spirit and scope of the invention.

Another application of the switchable gear according to the present disclosure is described below with reference to FIGS. 23-29. In this application, the switchable gear device of the present disclosure is used like a stop or lock device for a static position.

FIGS. 23 and 24 are diagrammatic view illustrating a conventional stop or lock device for a folding multi-position ladder, with the lock device shown in the closed (FIG. 23) and open (FIG. 24) states. These conventional folding ladders can be placed in various adjustable angle positions with push knobs locking a hinge and also adjusted in height using spring loaded “J” locks, as well as use 3-position multi-locking hinges. However, these conventional stop or lock arrangements for folding multi-position ladders suffer from the problems that the adjustments cannot be accomplished with high efficiency and also the degree of adjustment (e.g., the number of angles in which the ladder can be locked) is rather limited.

FIGS. 25-28 are rear and side cross-sectional perspective views illustrating an application of the switchable gear device according to the present disclosure as a stop or lock device for a static position, such as for a folding multi-position ladder, which overcomes the foregoing drawbacks in the conventional art.

As shown in FIGS. 25-28, the lock device, generally designated with reference numeral 100, includes a locking gear 12 and gear case 14 corresponding to the internal gear and external case described above for switchable gear device 10, a main shaft 15, a push knob 32 and spring 34. As best shown in FIG. 29, main shaft 15 is provided with external gear teeth 15 a.

FIGS. 25 and 26 show lock device 100 in a closed state in which gear teeth 12 b of locking gear 12 are in meshing engagement with gear teeth 15 a of main shaft 15 under the bias of spring 34 (in the left direction of FIG. 27). In this closed state, locking gear 12 is connected to main shaft 15 and gear case 14 is locked with main shaft 15, thereby preventing gear case 14 from undergoing rotation relative to main shaft 15.

FIGS. 27 and 28 show lock device 100 in an open state in which gear teeth 12 b of locking gear 12 are not in meshing engagement with gear teeth 15 a of main shaft 15. In this open state, locking gear 12 is not connected to main shaft 15 and gear case 14 is not locked with main shaft 15, thereby enabling gear case 14 to freely rotate relative to main shaft 15.

During operation, lock device 100 is activated by manually pushing and releasing push knob 32. When not activated, the lock device 100 is in the closed state as described above (FIGS. 25-26). When activated, the lock device 100 is in the open state as described above (FIGS. 27-28). To activate lock device 100, push knob 32 is manually pushed so that locking gear 12 slides into gear case 14 (in the right direction of FIG. 27) against the bias of spring 34 until locking gear 12 is disconnected from main shaft 15 (i.e., by releasing the meshing engagement between gear teeth 12 b of locking gear 12 and gear teeth 15 a of main shaft 15), thereby placing locking device 100 in the open state. While in the open state, gear case 14 is able to freely rotate relative to main shaft 15 to place it in any of a multitude of selected angular positions relative to main shaft 15 as illustrated in FIG. 29, for example. When the selected angular position is achieved, push knob 32 is released and locking gear 12 is connected back to main shaft 15 by the action of spring 34 and the lock device 100 is again placed in the closed state as described above.

In an exemplary embodiment, locking device 100 according to the present disclosure can be applied at multiple locations of a folding multi-position ladder as illustrated in FIG. 30. Locking device 100 allows one to lock the ladder in a multitude of angular positions (e.g., as shown in FIG. 29) and with high efficiency as compared to conventional ladder lock mechanisms, such as described above with reference to FIGS. 23 and 24.

FIGS. 31-39 show another exemplary application of the switchable gear device according to the present invention. In FIGS. 31-39, the switchable gear device, generally designated at 200, is applied to two articulated components in the general form of an articulated arm 220 (first component) and articulated arm 224 (second component) configured to undergo angular movement relative to one another.

FIG. 31 is a perspective view and FIG. 32 is a top view of switchable gear device 200 shown in an assembled state. Articulated arms 220, 224 include respective arm portions 204, 202 configured to be connected to various elements or objects requiring articulation at various angles relative one another. In this embodiment, arm portions 202, 204 are provided with an opening configured to receive such elements or objects. For example, the openings are configured to receive suitable wooden or metal beams which are integrally connected to arm portions 202, 204 by friction fit, welding, clamping and/or using suitable fasteners such as nails, bolts and/or screws to form a support structure for a scaffold, for example. It will be appreciated that articulated arms 220, 224 can be used for structures other than scaffolds, such as platforms, support beams, etc. By this construction and arrangement, it is appreciated that switchable gear device 200 according to the present invention can hold, support and/or extend any elements or objects attached to articulated arms 220, 224 giving it the ability to position the elements or objects at different angles relative one another.

FIGS. 33-39 illustrate various disassembled states of switchable gear device 200 in partial perspective and exploded views showing the various components and corresponding structural and positional relationships thereof, as further described below.

Articulated arm 220 has a gear case 222 extending from arm portion 204. Gear case 222 has the same internal construction as external case 14 described above with reference to FIGS. 1-15. In this embodiment, gear case 222 is formed in one piece with arm portion 204. Alternatively, gear case 222 and articulated arm 220, including arm portion 204, may be separate components which are integrally connected together using suitable connecting means. As shown in FIGS. 33, 37 and 38, arm portion 204 is provided with opening 221 for receiving any element/object as described above.

Referring to FIGS. 31-36, articulated arm 224 is provided with two housing portions 225 extending from arm portion 202. In this embodiment, housing portions 225 are formed in one piece with arm portion 202. Alternatively, housing portions 225 and articulated arm 224, including arm portion 202, may be separate components which are integrally connected together using suitable connecting means. Housing portions 225 are spaced-apart from one another to form a space 203 therebetween, as shown in FIGS. 31 and 34-36. Space 203 is configured to receive and accommodate gear case 222 of articulated arm 222, in the manner shown in FIGS. 31, 32, 38 and 39, so as to permit articulated arms 220, 224 to be moved and placed at various angles relative one another.

Referring to FIGS. 33-39, gear case 222 is configured to receive and accommodate switchable gears 210 (hereinafter also “internal gears”) each having the same construction (e.g., internal gear teeth) as internal gear 12 described above with reference to FIGS. 1-15. As described above for internal gear 12 and external case 14 in FIGS. 1-15, internal gears 210 and gear case 222 are configured so as to allow internal gears 210 to slide within and relative to gear case 222.

Each housing portion 225 of articulated arm 224 is configured to receive and support therein a main shaft 208 which has the same general construction (e.g., external gear teeth) as main shaft 16 described above with reference to FIGS. 1-15. Each main shaft 208 is supported by and retained in corresponding housing portion 225 by a washer 206 so that the external gear teeth of each main shaft 208 extends into space 203 of articulated arm 224 as shown in FIG. 34, for example. Each washer 206 has internal gear teeth configured to mesh with the external gear teeth of the corresponding main shaft 208. In the assembled state of switchable gear device 200, an outer surface of each washer 206 engages a lip of gear case 222 while an inner surface of each washer 206 engages an outer side of the corresponding main shaft 208. By this construction, relative sliding movement between articulated arms 220, 224 is prevented.

In the assembled state of switchable gear device 200, a portion of the external gear teeth of each main shaft 208 is configured to extend into gear case 222 from opposite ends thereof for driving engagement with the internal gear teeth of the corresponding internal gear 210, as shown for example in FIGS. 33-37, when internal gear teeth of internal gears 210 are slid into engagement with the external gear teeth of respective main shafts 208 as further described below. In FIGS. 33-37, main shafts 208 and internal gears 210 are disposed outside of gear case 222 for illustration purposes only to show how these components are configured for driving engagement with one another while positioned inside of gear case 222.

Internal gears 210 are configured for undergoing sliding movement within and relative to gear case 222 to selectively place them into engagement with and disengagement from main shafts 208. In a first state of switchable gear 200, internal gear teeth of internal gears 210 are disposed in meshing engagement with the external gear teeth of respective main shafts 208. In this first state, articulated arms 220, 224 are placed in a locked state and prevented from undergoing movement relative to one another. In a second state of switchable gear 200, internal gear teeth of internal gears 210 are completely disengaged from the external gear teeth of respective main shafts 208. In this second state, articulated arms 220, 224 are placed in an unlocked state and are permitted to undergo movement relative one another to position the corresponding elements or objects attached to articulated arms 220, 224 at different angles relative one another.

Switchable gear 200 is provided with switching means for switching between engagement and disengagement of internal gears 210 and main shafts 208 in the first and second states of switchable gear 200. Referring to FIGS. 34-39, the switching means comprises, for each internal gear 210, a push knob 212, a push rod 213 having one end connected to push knob 212 and another (opposite) end integrally connected to internal gear 210. For each internal gear 210, movement of push knob 212 in a direction towards (first direction) the corresponding housing portion 225 of articulated arm 224 causes internal gear 210 to slide inside gear case 222 in a direction which results in the disengagement of internal gear teeth of internal gear 210 from the external gears of the corresponding main shaft 208 to achieve the second state of switchable gear 200 as describe above. Likewise, for each internal gear 210, movement of push knob 212 in a direction away (second direction) from the corresponding housing portion 225 of articulated arm 224 causes internal gear 210 to slide inside gear case 222 in a direction which results in the internal gear teeth of internal gear 210 coming into meshing engagement with the external gears of the corresponding main shaft 208 to achieve the first state of switchable gear 200 as describe above.

In an exemplary embodiment, push rods 213 are in the form of threaded rods extending through a through hole of the corresponding main shaft 208 and securely threaded at one end to a threaded hole of the corresponding push knob 212. Each threaded rod 213 also engages the corresponding internal gear 210 and is securely retained thereto by a suitable fastener, (e.g., a threaded nut) denoted with reference numeral 211 in FIG. 34, that is securely engaged with the opposite end of threaded rod 213.

Each push knob 212 is associated with a biasing member 214 configured to bias push knob 212 in the second direction described above (i.e., in a direction away from the corresponding housing portion 225 of articulated arm 224) to maintain switchable gear 200 in the first state. By this arrangement, pressing push knobs 212 in the first direction described above (i.e., against the bias of springs 214) cause internal gear teeth of internal gears 210 to disengage from external gear teeth of respective main shafts 208 to achieve the second state of switchable gear 200 (i.e., permitting movement of articulated arms 220, 224 relative one another). In this embodiment, each biasing member 214 is in the form of a coil spring. It is understood, however, that other types of biasing members may be selected to perform the functions described without departing from the spirit and scope of the invention.

Referring to FIGS. 34-39, a stopper element 216 is securely mounted to an outer sidewall of each housing portion 225 for retaining the corresponding main shaft 208 within housing portion 225. Stopper element 216 is mounted to housing portion 225 using any suitable connecting means, such as by screws using holes 217 formed in stopper element 216.

Referring to FIGS. 31-29, removable knob covers 218 are provided for covering the respective push knobs 212. For each push knob 212, knob cover 218 has an opening providing access to a pressing surface of push knob 212, as shown in FIGS. 31, 33 and 37. Knob covers 218 also serve to prevent push knobs 212 from moving side to side and guide them during movement in the first and second directions as described above (i.e., to keep knob covers 218 aligned straight).

As best shown in FIGS. 34, 35 and 38, each knob cover 218 is provided with tab elements 219 configured for engagement with corresponding recessed portions 223 formed in stopper element 216 to removably mount knob cover 218 to stopper element 216.

FIGS. 31 and 32 show switchable gear device 200 in the first state described above, in which articulated arms 220, 224 are placed in a locked state and prevented from undergoing movement relative to one another. This is because in this first state the internal gear teeth of internal gears 210 are disposed in meshing engagement with the external gear teeth of respective main shafts 208 as described above. To switch switchable gear device 200 from the first state to the second state in which articulated arms 220, 224 are permitted to undergo movement relative one another, both push knobs 212 are pressed in the first direction (i.e., against the bias of biasing members 214) to cause internal gear teeth of internal gears 210 to slide inside gear case 222 until they are completely disengaged from the external gear teeth of respective main shafts 208. While push knobs 220, 224 are maintained in this pressed state, articulated arms 220, 224 can be moved relative one another to position the corresponding elements or objects attached to articulated arms 220, 224 at different preselected angles relative one another. After the desired relative angular position between elements or objects of the corresponding articulated arms 220, 224 is achieved, push knobs 212 are released by the biasing action of biasing members 214 (i.e., are caused to move in the second direction) to place switchable gear device 200 in the first state (i.e., to place articulated arms 220, 224 in the locked state). It will be appreciated that in the first and second states of switchable gear device 200, the engaging and disengaging actions between the main shafts 208 and corresponding internal gears take place inside gear case 222.

Without departing from the spirit and scope of the invention, it will be understood that the various components of the devices and systems according to the present disclosure described herein, including the switchable gear devices, transfer gear box and locking device, can be fabricated of any material required to achieve the intended purposes and functions. These materials include, for example, suitable metals such as steel and aluminum and as well as suitable plastic materials.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but are to be accorded the widest scope consistent with the principles and novel features disclosed herein. 

What is claimed is:
 1. A switchable gear device comprising: an internal gear; and an external gear configured to receive the internal gear and to be selectively connected to and disconnected from an external rotational shaft via the internal gear; wherein when received within the external case, the internal gear is configured to be selectively switched between an “ON” state and an “OFF” state; wherein in the “ON” state of the internal gear, the external case is connected to the external rotational shaft for undergoing rotation therewith; and wherein in the “OFF” state of the internal gear, the external case is disconnected from the external rotational shaft and does not undergo rotation therewith.
 2. The switchable gear device of claim 1; wherein the internal gear and external case are configured so as to allow the internal gear to slide within and relative to the external case to be selectively placed between the “ON” and “OFF” states.
 3. The switchable gear device of claim 1; wherein the internal gear is provided with a plurality of external gear teeth and the external case is provided with a plurality of gear slots for meshing engagement with the respective external gear teeth of the internal gear; wherein the meshing engagement between the external gear teeth and gear slots is such that the gear teeth are configured to slide along the respective gear slots to selectively place the internal gear between the “ON” and “OFF” states.
 4. The switchable gear device of claim 1; wherein the internal gear can be readily switched to the “ON” state by sliding the internal gear relative to the external case to a first position in which the internal gear is brought into engagement with the external rotational shaft to transmit rotational movement of the external rotational shaft to the external case; and wherein the internal gear can be readily switched from the “ON” state to the “OFF” state by sliding the internal gear relative to the external case to a second position in which the internal gear is disengaged from the external rotational shaft so that the rotational movement of the external rotational shaft is not transmitted to the external case.
 5. The switchable gear device of claim 4; wherein the internal gear has a tubular configuration and is provided with a plurality of internal gear teeth for meshing engagement with respective external gear teeth of the external rotational shaft when the internal gear is in the first position relative to the external case.
 6. The switchable gear device of claim 1; further comprising switching means for switching the internal gear between the “ON” state and the “OFF” state.
 7. The switchable gear device of claim 6; wherein the switching means comprises a hydraulic pressure device.
 8. The switchable gear device of claim 6, wherein the switching means comprises an electro-magnetic system.
 9. A transfer gearbox for 2WD to 4WD conversion having the switchable gear device according to claim
 1. 10. A lock device comprising: a locking gear; and a gear case configured to receive the locking gear and to be selectively connected to and disconnected from a main shaft via the locking gear; wherein when received within the gear case, the locking gear is configured to be selectively switched between a closed state and an open state; wherein in the closed state of the locking gear, the gear case is connected to the main shaft so that the gear case is not permitted to rotate relative to the main shaft; and wherein in the open state of the locking gear, the gear case is disconnected from the main shaft so that the gear case is allowed to rotate freely relative to the main shaft.
 11. The lock device of claim 10; wherein the locking gear is maintained in the closed state under the biasing action of a spring positioned within the gear case.
 12. The lock device of claim 11; further comprising a push knob for activating the lock device to disconnect the gear case from the main shaft by pushing the locking gear against the bias of the spring to place the locking gear in the open state.
 13. A folding multi-position ladder having the lock device of claim 10 for placing the ladder in various angular positions.
 14. The folding multi-position ladder of claim 13; wherein multiple ones of the locking devices are provided at selected positions of the ladder.
 15. A switchable gear device comprising: a first component; a second component configured to be mounted to the first component; a pair of internal gears mounted to the first component for undergoing sliding movement relative to the first component; a pair of main shafts mounted to the second component; and means for selectively causing the pair of internal gears to undergo sliding movement relative to the first component to engage the respective main shafts in a first state of the switchable gear device in which the first and second components are placed in a locked state and prevented from undergoing movement relative one another, and for selectively causing the pair of internal gears to undergo sliding movement relative to the first component to disengage from the respective main shafts in a second state of the switchable gear device in which the first and second components are placed in an unlocked state and permitted to undergo movement relative one another.
 16. The switchable gear of claim 15; wherein the means for selectively causing comprises, for each of the pair of internal gears, a push knob, a push rod having one end integrally connected to the push knob and another end integrally connected to the internal gear, and a biasing member for biasing the push knob, the push rod and the internal gear in a direction in which the first and second components are placed in the locked state.
 17. The switchable gear of claim 16; wherein the push knobs and the push rods are configured to be pushed against the bias of the biasing member to cause the internal gears to undergo sliding movement relative to the first component to disengage from the respective main shafts so that the first and second components are placed in the unlocked state and are capable of being moved relative one another.
 18. The switchable gear of claim 16; wherein the first component has a gear case configured to house the pair of internal gears while allowing the internal gears to undergo sliding movement relative to the gear case.
 19. The switchable gear of claim 18; wherein the second component has a pair of housing portions for securely retaining therein the respective main shafts.
 20. The switchable gear of claim 19; further comprising knob covers configured to be removably mounted to the respective housing portions of the second component, each of the knob covers having an opening providing access to a pressing surface of the corresponding push knobs. 